It's second generation of dual processor, it has better performance than the old core duo.
Many test prove that the core 2 duo is better in different percentage performance from core duo around 9% to 60%, depend on what kind of application that you run.
If you already have core duo no need to upgrade to core 2 duo.
but if you're going to buy new one I'll recommend core 2 duo because the price almost the same.

